Many of metal materials, such as aluminum, magnesium, iron, copper, zinc, nickel and alloys thereof, are widely used as parts and components for automobiles, parts and components for household electric and electronic appliances, construction materials, beverage containers and like after providing their surfaces with various resin coating layers to improve their protection performance and external attractiveness and then applying extensive forming to them as mentioned above.
A variety of properties are required upon using metal materials in the above-mentioned fields. To meet such property requirements, diverse resin coating layers are applied to the surfaces of the metal materials depending on their application purposes. As methods for forming such resin coating layers, methods such as coating, film lamination and printing can be mentioned. Basically speaking, excellent corrosion resistance, interlayer adhesion and solvent resistance (waterproofness) of materials are properties required not only in the field of metals but also in other fields.
Upon coating a material such as a metal, the material is coated on a surface thereof, for example, with a solvent-based coating composition, water-based coating composition or powder coating composition, and is then dried at room temperature or under heat to form a coating (resin coating layer) on the surface such that the coating composition is allowed to exhibit functions which the coating composition is inherently equipped with. Solvent-based coating compositions have been used widely for many years. With a view to reducing the pollutant load on the environment, however, there is an increasing move toward water-based coating compositions or powder coating compositions or a method making use of films such as lamination or the like. Nonetheless, coating methods making use of solvent-based coating compositions are still used these days in a large majority of fields.
Especially in the substrate treatment (which may hereinafter be called “priming”) of metal materials, chromate treatment making use of chemicals, which contain hexavalent chromium, has been used widely for many years for its economy. In recent years, however, there is an ever-increasing move on a worldwide level toward not only reductions in the influence to the human body but also global environmental conservation, such as the regulations on use of toxic metals (compounds, ions) such as hexavalent chromium, lead and cadmium in Europe and the PRTR (Pollutant Release and Transfer Register) and the disclosure of a listing of environmental hormone substances in Japan.
Under the circumstances as described above, there is ever-increasing recognition of a crisis about adverse effects on the human body and environment. Many technologies capable of substituting for hexavalent chromium which is generally used as a surface treatment composition, that is, many substrate treatment compositions for metal materials, said compositions making absolutely no use of hexavalent chromium, have been proposed accordingly. Substrate treatment compositions free of hexavalent chromium include those containing as principal components organic compounds such as water-soluble resins or emulsion resins, those containing as principal components inorganic compounds of metals other than hexavalent chromium or heavy metals, and composite-type ones containing both of the components. Also known are substrate treatment techniques making use of these substrate treatment compositions and metal materials subjected to such substrate treatments. Further, such substrate treatment methods include “chemical conversion treatments” in each of which a substrate treatment composition and a metal materials are chemically reacted with each other, “dry-in-place treatments” in each of which a substrate treatment composition itself is subjected to a chemical reaction by causing a solvent to evaporate under heat, and “electrolysis treatments” in each of which electricity is fed from an external power source to a metal material to subject it to a chemical reaction.
In particular, chemical conversion treatments and coating treatments are economically advantageous as they do not use electricity. With respect to the components of substrate treatment compositions, many conventional substrate treatment compositions are known to contain inorganic compounds as principal components and are also using organic compounds in combination to supplement properties not satisfied by the inorganic compounds. For example, JP 11-350157 A discloses a substrate treatment composition which is composed of an Al-phosphoric acid compound, at least one of Mn, Mg, Ca and Sr compounds, a sol of SiO2, and a particular water-based organic resin emulsion or water-soluble resin.
JP 10-1789 A discloses a substrate treatment composition containing an organic high-molecular compound, such as a nitrogen-containing acrylic resin, urethane resin, phenolic resin, olefin resin or amide resin, and polyvalent anions in specific amounts; a substrate treatment method; and treated metal materials. Further, JP 10-46101 A discloses a coated metal material the surface of which has been treated with a water-based treatment composition containing a particular phenolic resin in combination with a phosphoric acid compound and an organosilicon compound; and a production process thereof.
In addition, JP 11-140691 A contains a disclosure about a substrate treatment method, a treated steel plate, and a steel plate making use of the treated steel plate and coated with a thermoplastic resin. Concerning the treatment of a substrate, it also discloses a technique in which the substrate is treated with a silane coupling agent. Furthermore, JP 8-27595 A discloses a treatment method which comprises controlling the temperature of a phosphate salt, water-soluble resin and surfactant of specific concentrations to a specific temperature, immersing an aluminum alloy plate, and applying cathodization and anodization in combination.
The above techniques are described as applied to metal materials subjected to specific treatments by methods such as electrolysis, chemical conversion treatment or coating, or as applied to resin-coated metal materials obtained by laminating films on the metal materials or coating the metal materials. However, all of these metal materials are those applied with treatment compositions which are free of hexavalent chromium, and the resin coating layers of these metal materials are insufficient in all of durable adhesive properties, solvent resistance and the corrosion resistance of the metal material under severe environments. Electrolytic methods, on the other hand, require substantial energy cost, and are not preferred economically. Under the current circumstances, there is accordingly no technique that uses a substrate treatment composition free of hexavalent chromium and can provide a satisfactory metal material excellent in the adhesive properties and solvent resistance of its resin coating layer and in corrosion resistance.
An object of the present invention is, therefore, to overcome the above-described various problems of the conventional art, and to provide a water-based, substrate treatment composition and a substrate treatment method, which can improve especially the interlayer adhesion between a metal material and a resin coating layer such as a film or coating, the solvent resistance of the resin coating layer and the corrosion resistance of the metal material or the like, and also a treated material.